This invention relates to silver halide photographic light-sensitive materials and, more particularly, to photographic light-sensitive materials providing extremely high-contrast negative images and good dot image quality.
It is known to add hydrazine compounds to silver halide photographic emulsions or developers, as described, for example, in U.S. Pat. No. 3,730,727 (developer containing ascorbic acid and hydrazine), U.S. Pat. No. 3,227,552 (the use of hydrazine as an auxiliary developing agent for obtaining direct positive color images), U.S. Pat. No. 3,386,831 (containing .beta.-monophenylhydrazine of an aliphatic carboxylic acid as a stabilizer for silver halide light-sensitive materials), and U.S. Pat. No. 2,419,975 as well as in Mees and James, The Theory of the Photographic Process, 3rd Edition, page 281 (1966), etc.
In particular, U.S. Pat. No. 2,419,975 discloses that high-contrast negative images are obtained by the addition of hydrazine compounds. This patent describes that extremely high-contrast photographic characteristics, such as a gamma (.gamma.) of more than 10, can be obtained by adding a hydrazine compound to a silver chlorobromide emulsion and developing at a pH as high as 12.8. However, a strong-alkaline developer having a pH of nearly 13 is susceptible to air oxidation and is too unstable to be stored or used for long period of times.
Super-high-contrast photographic characteristics of more than 10 in gamma are extremely useful, in either negative image or positive image, for the photographic reproduction of continuous gradation images as dot images, which are useful for making printing plates, or for reproduction of line images. For the purpose of obtaining such photographic characteristics, a process has generally been used wherein a silver chlorobromide emulsion containing more than 50 mol%, and preferably more than 75 mol%, silver chloride is used, and is developed by a hydroquinone-containing developer having an extremely low (usually lower than 0.1 mol/liter) effective density of sulfite ion (hereinafter "lithographic developer").
However, in such a process the developer is very unstable due to the low sulfite ion concentration in the developer, and hence cannot stably be stored for more than 3 days.
Moreover, since processes as described above require the use of silver chlorobromide emulsions having a relatively high silver chloride content, it has been impossible to obtain a high sensitivity by such processes. Therefore, it has been strongly desired to obtain superhigh-contrast photographic characteristics useful for the reproduction of dot images and line images using a highly sensitive silver halide emulsion and a stable developer.
We have previously disclosed that extremely high contrast negative image is obtained using a stable developer by developing a silver halide photographic material in the presence of some types of acylhydrazine compound, such as R.sup.1 NHNHCOR.sup.2 (wherein R.sup.1 represents an aryl group, R.sup.2 represents hydrogen, a phenyl group and an alkyl group) and X.sup.1 -Ar.sup.2 -B).sub.n Ar.sup.1 --NHNHCOR.sup.2 (wherein X.sup.1 represents a group having --CS--NH-- unit, Ar.sup.1 and Ar.sup.2 each represents a divalent aromatic group, B represents a divalent linking group, n represents 0 or 1 and R.sup.2 is the same as above), in U.S. Pat. No. 4,168,977, West German Patent Publication (ALS) No. 2,725,743 and West German Patent Application (OLS) No. 2,941,428. However, the acylhydrazine compounds used therein have proved to possess some defects.
One of these defects is that since the pH of the developer most suitable for obtaining good contrast images and dot images is relatively high, viz., higher than about 11, the stability of the developer when stored for a long period of time is still considered insufficient, although the stability is remarkably high as compared with conventional lithographic developers.
Since as the pH of a developer is lowered, the occurrence of oxidation of developing agent decreases, and the stability of the developer stored for a long period of time increases, more active hydrazine compounds providing high contrast images and good dot image quality at low pH have been keenly desired.
A second defect is that using the hydrazine compounds previously disclosed it is difficult to obtain good dot quality and extremely high-contrast image using silver halide emulsions having relatively large grain sizes (e.g., a mean grain size of larger than 0.7 .mu.m).
This is undesirable because increasing the grain size of the silver halide is a very fundamental means for increasing the sensitivity of silver halide emulsion, and hence compounds are desired which provide high-contrast even in case of using silver halide emulsions having large silver halide grains.
A third defect is that the screen range obtained by developing a silver halide photographic material in the presence of an acylhydrazine compound disclosed previously is smaller than screen range obtained by using conventional lithographic light-sensitive materials and lithographic developers.
By the term "screen range" is meant a difference between a logarithmic value of the exposure amount for providing a larger dot area (usually dot having a blacken area of 95%) and a logarithmic value of the exposure amount for providing a smaller dot area (usually dot having a blacken area of 5%) in the case of converting the change of a density having continuous gradation of original image into the change in dot area by means of exposure through a contact screen, and the larger the screen range is, the more preferable is, because of being capable of being uniformly converted as the change in dot area from the high density portion to the low density portion.
For obtaining high-quality prints having good gradation reproduction, it is preferred that the dot gradation is as soft as an extent obtained by a combination of a lithographic photographic light-sensitive material and lithographic development, but since the acylhydrazine compounds previously disclosed give considerably hard dot gradation (i.e., slightly poor gradation reproduction), compounds capable of providing softer dot gradation have been desired.